In many aircraft structures and assemblies, such as engine nacelles, jet thrust reverser cowlings, auxiliary power units and other applications and locations, a fire barrier seal is utilized between opposing faces or parts. These opposing parts may be opened and closed repeatedly during aircraft operation or maintenance procedures. Typically, the seal must follow a long, usually enclosed and typically non-linear path around the structure, and provide a thermal barrier that will withstand particular conditions, such as an exposure to 2000.degree. F. for in excess of 15 minutes. This standard test condition is imposed in order to assure protection for the occupants of the aircraft or for critical machinery against fires of less than catastrophic nature, and to provide adequate thermal protection for control or escape measures.
Prior barrier seals heretofore used in these applications have typically employed an extruded body of high temperature resin, such as hollow fluorosilicone cylinder having an integral flange or base on one side, and covered by a temperature resistant material such as fiberglass fabric or batt material. Prior constructions have been deficient in one of a number of respects, such as being too costly, requiring periodic replacement or providing an inadequate seal. It is difficult to uniformly wrap or adhere external insulation material to the internal tube, and so the external surface is not often smooth enough to make a seal. In addition, the seals, typically known as "bulb seals", are repeatedly compressed in normal use, and do not restore to their proper shape and maintain the seal. Furthermore, such seal structures often have marginal thermal resistance and burn out in an excessively short time. The capability of being compressed many thousands of times while still providing a good thermal barrier to fire is thus difficult to achieve. More rigid seals are not acceptable, because most parts using such seals have to be manipulated manually and excessive force would have to be applied.